so they list a whole bunch of technologies that might reduce the carbon emissions. in principle, they could do that. and then, actually, when you talk to the authors, they say, we're -- are there any more wedges? they say, oh yeah, there are a lot more wedges. at least we got tired. you know. so -- but those things were theoretical. what will cause those in reality, you put a price on carbon, some of those wedges would really be great stuff and they would -- you'd pass a tipping point that would really take a big chunk of the energy. and some of them wouldn't work out at all. but, you know, you just can't do it with theoretical exercises. the way that it will work -- sorry, it's a broken record, but you got to have a price on carbon. >> and so -- [laughter] >> right. but you talk about the marketplace. one of the ways that u.s. has reduced its emissions is through switching from coal to gas, and that was government innovation 30 years ago developing some tracking -- fracking technology that no one saw a few years ago, and -- that proponents would say that that switc